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Abstract Volcanic evolution in ocean island settings is often controlled by variations in the chemistry and volumetric flux of magma from an underlying mantle plume. In locations such as Hawaiʻi or Réunion, this results in predictable variations in magma chemistry, the rate of volcanic activity, and the depth of magma storage with volcanic age and/or distance from the centre of plume upwelling. These systems, however, represent outliers in global plume volcanism due to their high buoyancy flux, frequent eruptions, and large distance from any plate boundary. Most mantle plumes display clear interaction with nearby plate boundaries, influencing the dynamics of solid plume material in the upper mantle and the distribution of melt across regions of active volcanism. Yet, the influence of plume–ridge interaction and plume–ridge distance on the structure, characteristics, and evolution of magma storage beneath ocean island volcanoes remains under constrained. In this study, we consider the evolution of magmatic systems in the Galápagos Archipelago, a region of mantle plume volcanism located 150–250 km south of the Galápagos Spreading Centre (GSC), focusing on the depth of magma storage during the eastward transport of volcanic systems away from the centre of plume upwelling. Geochemical analysis of gabbro xenoliths from Isla Floreana in the southeastern Galápagos suggest that they formed at ~2–2.5 Ma, when the island was located close to the centre of plume upwelling. These nodules, therefore, provide rare insights into the evolution of volcanic systems in the Galápagos Archipelago, tracking variations in the magma system architecture as the Nazca plate carried Isla Floreana eastwards, away from the plume centre. Mineral thermobarometry, thermodynamic modelling, and CO2 fluid inclusion barometry reveal that Isla Floreana’s plume-proximal stage of volcanic activity—recorded in the gabbro xenoliths—was characterized by the presence of high-pressure magma storage (>25 km), below the base of the crust. In fact, we find no petrological evidence that sustained, crustal-level magma storage ever occurred beneath Isla Floreana. Our results contrast with the characteristics of volcanic systems in the western Galápagos above the current centre of plume upwelling, where mid-crust magma storage has been identified. We propose that this change in magmatic architecture of plume-proximal volcanic centres in the Galápagos—from high-pressure mantle storage at 2.5 Ma to mid-crustal storage at the present day—is controlled by the variations in plume–ridge distance. Owing to the northward migration of the GSC, the distance separating the plume stem and GSC is not constant, and was likely <100 km at 2.5 Ma, significantly less than the current plume–ridge distance of 150–250 km. We propose that smaller plume–ridge distances result in greater diversion of plume-material to the GSC, ‘starving’ the eastern Galápagos islands of magma during their initial formation and restricting the ability for these systems to develop long-lived crustal magma reservoirs. 

Mineral and fluid inclusion data collected from a suite a gabbro xenoliths found on the island of Floreana in the southern Galapagos. Mineral chemistry is primarily determined by SEM-based EDS and WDS analysis with LA ICP-MS used to determine the clinopyroxene trace element contents. Microthermometry and Raman analysis are used to assess the composition and CO2 density of clinopyroxene and plagioclase hosted fluid inclusions. 

Luo et al.1 present exciting new data on lunar basalt samples erupted at ~2 Ga, and brought to Earth by the Chang’e-5 (CE-5) mission. These samples offer important new opportunities to understand lunar magmatic systems. Luo et al.1 use Clinopyroxene-Liquid (Cpx-Liq) thermobarometry and pMELTS modelling of mineral compositions to determine the pressures (P) and temperatures (T) of magma storage on the moon. However, in this comment we discus the large analytical errors associated with their measurements, and the implications for their intepretation. 

Abstract The emergence of the “mush paradigm” has raised several questions for conventional models of magma storage and extraction: how are melts extracted to form eruptible liquid-rich domains? What mechanism controls melt transport in mush-rich systems? Recently, reactive flow has been proposed as a major contributing factor in the formation of high porosity, melt-rich regions. Yet, owing to the absence of accurate geochemical simulations, the influence of reactive flow on the porosity of natural mush systems remains under-constrained. Here, we use a thermodynamically constrained model of melt-mush reaction to simulate the chemical, mineralogical, and physical consequences of reactive flow in a multi-component mush system. Our results demonstrate that reactive flow within troctolitic to gabbroic mushes can drive large changes in mush porosity. For example, primitive magma recharge causes an increase in the system porosity and could trigger melt channelization or mush destabilization, aiding rapid melt transfer through low-porosity mush reservoirs.